Bubble generating arrangement, system &amp; method

ABSTRACT

An arrangement to generate foam, the arrangement comprising: a porous material; a plenum having an aperture disposed to supply gas to the porous material; and a tub containing a foamable liquid, disposed to at least partially submerge the porous material in the foamable liquid; foam being generated as the gas is injected via the porous material into the foamable liquid.

PRIORITY INFORMATION

This application claims priority under 35 U.S.C. §120 upon anon-provisional U.S. patent application having Ser. No. 10/901,418 filedJul. 30, 2004, the disclosure of which is incorporated herein in itsentirety.

BACKGROUND OF THE PRESENT INVENTION

Foaming technologies for use in fire suppression and fire fighting aregenerally known. Such foaming technologies are typically classified inone of two categories of foam, namely air-aspirated foam andcompressed-air foam.

The older of the two is air-aspirated foam. A stream of foamablesolution is piped to a nozzle at a given pressure and at a given speed.The nozzle is configured so as to produce an increase in the speed andthe turbulence, and consequently a drop in the pressure, of the foamablesolution. The pressure drop draws air into the nozzle where it becomesentrained by the turbulence of the foamable solution. A stream of liquid(albeit containing entrained air) is ejected at the nozzle.

The newer of the two is compressed-air foam. Compressed air is injectedinto the stream of foamable solution inside the pipe away from thenozzle. That is, compressed air forces its way into the foamable streamaway from the nozzle rather than being aspirated (or drawn) into thestream of foamable solution at the nozzle. Here, similarly, a stream ofliquid (albeit containing entrained air) is ejected at the nozzle.

SUMMARY OF THE PRESENT INVENTION

An embodiment of the present invention provides an arrangement togenerate foam, the arrangement comprising: a porous material; a plenumhaving an aperture disposed to supply gas to the porous material; and atub containing a foamable liquid, disposed to at least partiallysubmerge the porous material in the foamable liquid; foam beinggenerated as the gas is injected via the porous material into thefoamable liquid.

Another embodiment of the present invention provides a system tosuppress fire within a substantially enclosed volume, comprising: afirst plurality of foam generators, each foam generator includingstream-forming means for forming a second plurality of low-speed streamsof gas and for introducing the same into a foamable liquid, the foamableliquid being at about atmospheric pressure.

Another embodiment of the present invention provides a method ofgenerating foam comprising: providing a porous material; at leastpartially submerging the porous material in a foamable liquid; forcing agas into the foamable liquid via the porous material.

Another embodiment of the present invention provides an arrangement togenerate foam, the arrangement comprising: a tub containing a foamableliquid; stream-forming means for forming a plurality of low-speedstreams of gas and for introducing the same into the foamable liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view block diagram of a bubble generating systemaccording to an embodiment of the present invention.

FIG. 2 is a quasi cross-section of a bubble generator according to anembodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention will be described more fully with reference to theaccompanying drawings, in which example embodiments of the presentinvention are shown. It should be understood, however, that exampleembodiments of the present invention described herein can be modified inform and detail without departing from the spirit and scope of thepresent invention. Accordingly, the embodiments described herein areprovided by way of example and not of limitation, and the scope of thepresent invention is not restricted to the particular embodimentsdescribed herein.

In particular, the relative thicknesses and positioning of structures orregions may be reduced or exaggerated for clarity. In other words, thefigures are not drawn to scale. Further, a structure is considered asbeing formed “on” another structure when formed either directly on thereferenced structure or formed on other structures overlaying thereferenced structure.

Reference number similarities from one figure to the next suggest atleast similar components/items.

FIG. 1 is a top view block diagram of a bubble generating system 102according to an embodiment of the present invention.

In FIG. 1, bubble generating system 102 is disposed within asubstantially enclosed volume 100, e.g., the interior of a warehouse, acompartment of a ship, etc. System 102 can include: a plurality ofbubble generators 3, each of which can include a porous material 2; asource 1 of gas 7, e.g., air; a network 104 of pipes that supply gas 7to bubble generators 3; a source 4 of foamable liquid 5 (i.e., asolution which can form a foam when mixed with a gas); and a network 108of pipes that supply foamable liquid 5 to bubble generators 3.

Network 104 can include a plurality of plenums 106 that connect to theplurality of bubble generators 3, respectively. Source 1 can be arrangedto draw gas, e.g., from outside of, and introduce it into, volume 100.Network 108 can include a plurality of branches 10 that connect to theplurality of bubble generators 3, respectively.

The plurality of foam generators 3 can be dispersed within thesubstantially enclosed volume 100. For example, at least a majority ofthe plurality of foam generators 3 can be dispersed proximate to aceiling region (not depicted) of volume 100.

Foamable liquid 5 can be an aqueous solution that includes at least anagent to reduce the surface tension of water. For example, foamableliquid 5 can be PYROCOOL® brand, formula FEF solution, made available byPyrocool Technologies Inc.

FIG. 2 is a quasi cross-section of a bubble generator according to anembodiment of the present invention. The quasi cross-sectionalperspective of FIG. 2 corresponds to sectional II-II′ of FIG. 1.

In FIG. 2, bubble generator 3 includes tub 20 which can be used tocontain foamable liquid 5 received from branch 110 (not depicted in FIG.2). In tub 20, foamable liquid 5 can be at about atmospheric pressure.An end of plenum 106 can be disposed in tub 20, more an end portion ofplenum 106 that includes an aperture 22 can be disposed in foamableliquid 5 contained in tub 20. Aperture 22 can be any shape, e.g., inFIG. 2 it is depicted as rectangular.

Plenum 106 can be arranged so that aperture 22 can supply gas 7 toporous material 2. More particularly, at least a portion of porousmaterial 2 can be fit as a plug into aperture 22, e.g., FIG. 1 shows anexample circumstance in which the entirety of porous material 2 isfitted into aperture 22. Tub 20 is disposed to at least partiallysubmerge porous material 2 in foamable liquid 5, e.g., FIG. 2 shows anexample circumstance in which porous material 2 is fully submerged infoamable liquid 5.

Porous material 2 can be a sponge, aerogel, e.g., silica aerogel, aporous resin, etc. Porous material 2 includes pores. More specifically,porous material 2 includes at least one of macropores, mesopores andmacropores. Pore size is a significant factor in determining the size ofthe bubbles produced. The size of the bubbles will vary depending uponthe size of volume 100, the chemical composition of foamable liquid 5and the capacity of source 1 & network 104.

Foam generation will now be described.

Gas 7 is pumped by source 1 via network 104 such that plenums 106deliver gas to porous material 2 at apertures 22 in plenums 106. Withoutbeing bound by theory, the porous nature of porous material 2 acts toform a plurality (if not a multitude) of streams of gas, and thesubmergence of porous material 2 causes the streams to be introduceddirectly into foamable liquid 5, where bubbles 6 are formed. In otherwords, gas 7 is injected via porous material 2 into foamable liquid 5,and the speed of gas 7 in the streams is relatively low, e.g., ascontrasted to the Background Art foam generation systems. Gas 7experiences a pressure drop across porous material 2. Bubbles 6 risewithin foamable liquid 5 and eventually escape or bubble up and out soas to enter the atmosphere within substantially enclosed volume 100. Incontrast to the Background Art air-aspirated and compressed-airtechnologies, a liquid stream having entrained gas is not being ejectedfrom porous material 2.

Some example calculations are provided for a specific albeit sampleimplementation of system 102. Suppose that substantially enclosed volume100 represents: R (cubic feet), and that system 100 should be able tofill volume 100 with bubbles in a time T_(f) minutes, e.g., T_(f)=3.Thus, system 102 must be capable of generating R/T_(f) of bubbles (inunits of CFM). Assuming that there are N bubble generators such thatthere are N apertures 22, and further describing apertures 22 asrectangular with a length L and a width D (D, e.g., is 0.24 feet (ft),then L=R/(T_(f)*N*V*D), where W is the speed (in feet per minute (FM))needed to achieve R. If V=200,000 ft³, T_(f)=3 minutes, N=20, D=0.25 ftand W=1000 ft/min, then L=14 ft.

An ideal rate of foam generation, R_(i), can be scaled by compensationfactors to obtain a desired rate of foam generation, R_(d). At least twocompensation factors can be: C_(s), representing a compensation factorfor the shrinkage that foam typically undergoes, e.g., C_(s)=1.15; andC₁, representing a compensation factor for leakage of the foam from thesubstantially enclosed volume 100, e.g., C₁=1.1 (for slight leakage). Assuch, R_(d)=C_(s)R_(i), R_(d)=C₁R_(i) or R_(d)=(Cs+C₁)R_(i).

Some further example calculations are provided for a second specificalbeit sample implementation of system 102. Suppose that the density offoamable liquid 5 is almost the same as water, the difference beingnegligible. Then, if porous material 2 is disposed to a depth of about0.5 inches in foamable liquid 5, then the minimum or threshold gas speedV_(b) (at the point where gas 7 is injected via porous material 2 intofoamable liquid 5) needed to generate a bubble within foamable liquid 5is calculated as follows.V _(b)=√{square root over (2*(ρ_(H2O)/ρ_(gas))*g*h))}where ρ_(H2O) is the density of water (assumed to be substantially thesame as the density of foamable liquid 5), ρ_(gas) is the density of gas7, g is the acceleration due to gravity and h is the height (depth) ofthe foamable liquid 5. Taking ρ_(H2O)=1000 kg per cubic meter, takinggas 7 to be air such that ρ_(gas)=1.225 kg per cubic meter, g≈10 meterper square second and h=0.5 inches, then V_(b)≈14 meters persecond≈about 30 MPH (miles per hour).

While the speed of gas that exits porous material 2 into foamable liquid5 should be at least V_(b), as a practical matter there is also amaximum speed (V_(max)) above which bubble formation is retardedsubstantially. For example, V_(max)≦(≈1.5V_(b)), more particularly e.g.,V_(max)≈1.2V_(b). It should be understood that the density of foamableliquid 5 influences the value of V_(b).

Continuing the example calculations regarding the second specific albeitsample implementation of system 102, assume that substantially enclosedvolume 100 has a value VOL=200,000 ft³ and that T_(f)=3 minutes. Furtherassume that network 104 (including plenums 106) is ideal such that nopressure drops are experienced therein, and that gas source 1 is a fanassembly with an 8 inch diameter (Area, A=0.349 ft²) that delivers gasat a speed S=150 mph (miles per hour) thus yielding a capacity of about4200 CFM (cubic feet per minute)=0.349*150*3*1600/60. To fill VOL intime T_(f), the air speed will be S=200000/3/60/0.349=3184 feet persec=2387 mph. Therefore, such an instance of system 100 would need about16 gas sources 1. The total effective area of holes which porousmaterial 2 represents to gas 7 blowing therethrough would beA_(effective)=0.349*150/30=1.7 square feet.

FIG. 2 has depicted the example circumstance for system 102 in whichaperture 22 can facilitate a downward flow of gas 7 into foamable liquid5 via porous material 5. Alternatively, e.g., system 100 can be arrangedlike, e.g., a sink in a kitchen/bathroom such that plenum 106 andaperture 22 can be positioned analogously to the drain pipe and thedrain hole of the sink, and porous material 2 can be positionedanalogously to a stopper inserted into the drain hole. Such analternative arrangement has gas 7 flowing substantially continuallyupward from plenum 106. In contrast, system 102 of FIG. 2, gas flowsdownward from plenum 106 and then changes direction, moving upward, inthe form of bubbles when it becomes enclosed inside walls of foamingliquid 5 in tub 20.

Embodiments of the present invention having been thus described, it willbe obvious that the same may be varied in many ways. Such variations arenot to be regarded as a departure from the spirit and scope of thepresent invention, and all such modifications are intended to beincluded within the scope of the present invention.

1. An arrangement to generate foam, the arrangement comprising: a porous material; a plenum having an aperture disposed to supply gas to the porous material; and a tub containing a foamable liquid, disposed to at least partially submerge the porous material in the foamable liquid; foam being generated as the gas is injected via the porous material into the foamable liquid.
 2. The foam-generating arrangement of claim 1, wherein: the porous material is one of a sponge, an aerogel and a porous resin.
 3. The foam-generating arrangement of claim 1, wherein: the porous material includes at least one of macropores, mesopores and macropores.
 4. The foam-generating arrangement of claim 1, wherein the pressure of the foamable liquid is about atmospheric pressure.
 5. The foam-generating arrangement of claim 1, wherein at least a portion of the porous material is fitted as a plug into the aperture.
 6. The foam-generating arrangement of claim 1, wherein the gas is air.
 7. The foam-generating arrangement of claim 1, wherein a maximum speed V_(max) at which the gas is injected into the foamable liquid is V _(max)≦(≈1.5V _(b)), where V_(b) is the minimum speed at which injection of the gas into the foamable liquid can achieve bubble formation.
 8. The foam-generating arrangement of claim 7, wherein V_(max)≈1.2V_(b).
 9. A system to suppress fire within a substantially enclosed volume, the system comprising: a first plurality of foam generators, each foam generator including stream-forming means for forming a second plurality of low-speed streams of gas and for introducing the same into a foamable liquid, the foamable liquid being at about atmospheric pressure.
 10. The system of claim 9, wherein each stream-forming means includes a porous material via which the gas is introduced into the foamable liquid.
 11. The system of claim 10, wherein the porous material is at least partially submerged in the foamable liquid.
 12. The system of claim 9, wherein the second plurality of low-speed streams is a multitude.
 13. The system of claim 9, further comprising: a source of gas; a plurality of plenums arranged to conduct gas to the plurality of stream-forming means, respectively.
 14. The system of claim 9, wherein the first plurality of foam generators are dispersed within the substantially enclosed volume.
 15. The system of claim 9, wherein at least a majority of the first plurality of foam generators are dispersed proximate to a ceiling region of the enclosed volume.
 16. The system of claim 9, wherein the low-speed of the streams of gas has a maximum V_(max), V _(max)≦(≈1.5V _(b)), where V_(b) is the minimum speed at which introduction of the gas into the foamable liquid can achieve bubble formation.
 17. The system of claim 16, wherein V_(max)≈1.2V_(b).
 18. A method of generating foam comprising: providing a porous material; at least partially submerging the porous material in a foamable liquid; forcing a gas into the foamable liquid via the porous material.
 19. The method of claim 18, further comprising: using the foamable liquid at about atmospheric pressure.
 20. The method of claim 18, further comprising: using air as the gas.
 21. The method of claim 18, wherein a maximum speed V_(max) at which the gas is forced into the foamable liquid is V _(max)≦(≈1.5V _(b)), where V_(b) is the minimum speed at which the gas can be forced into the foamable liquid and still can achieve bubble formation.
 22. The method of claim 21, wherein V_(max)≈1.2V_(b).
 23. An arrangement to generate foam, the arrangement comprising: a tub containing a foamable liquid; stream-forming means for forming a plurality of low-speed streams of gas and for introducing the same into the foamable liquid.
 24. The foam-generating arrangement of claim 23, wherein the plurality of low-speed streams is a multitude.
 25. The foam-generating arrangement of claim 23, wherein the low-speed of the streams of gas has a maximum V_(max), V _(max)≦(≈1.5V _(b)), where V_(b) is the minimum speed at which introduction of the gas into the foamable liquid can achieve bubble formation.
 26. The foam-generating arrangement of claim 25, wherein V_(max)≈1.2V_(b). 